184 University of California Publications in Geology [Vol. 7 



sandstone no longer predominates but is largely replaced by shale, 

 yet below the lowermost lower Miocene fossils found." 



With such a lack of a definite division plane between shales 

 and sandstones, or rather such a gradation between them, the 

 only logical procedure would seem to be to construct the series 

 on the plan of its nearby, definitely determined and lithologically 

 similar correlative. 



Further evidence of this relationship was obtained by an 

 examination of the "Upper Sespe" for palaeontological data. 

 At various horizons fossils were found, although mostly in a 

 broken condition and not distinctly determinable. About fifty 

 feet above the base of the "Upper Sespe" in the hills to the 

 south of Tar Creek, where this formation is about 500 feet thick 

 and is mapped 8 as a strip one-half to three-quarters of a mile 

 wide, a layer was found made up practically entirely of one 

 species, Scutella fairbanksi Merriam, 9 which is considered a 

 characteristic fossil of the Vaqueros zone. 



There seems, therefore, no reason for hesitating to disconnect 

 these sands from the Sespe group and unite them definitely with 

 the Vaqueros-Monterey. The exceptional nature of the opening 

 of this period of sedimentation in the Santa Clara region there- 

 fore disappears. 



The Sespe Formation 



The term Sespe was originally used by Watts 10 in the form 

 "Sespe brownstone formation," which he said "consists of sand- 

 stone shales and conglomerate all being more or less brown in 

 color." Eldridge and Arnold 11 employed this term in the ex- 

 pression "Sespe formation," as shown in the columnar section 

 above given and added to the brownstone formation the yellowish 

 (ochreous) sandstones above and a white sandstone below. 



The exact relationship of the Sespe brownstone formation 

 to the Vaqueros the writer did not work out. In a general way 



x Bull. 309, Plate I. 



» This determination was kindly checked by Professor J. C. Merriam. 

 io Bull. Cal. State Mining Bureau, no. 11, pp. 11 and 12. 

 u U. S. Geol. Surv. Bull. 309, pp. 7-12. 



